Chlorine

Chlorine (from the Greek language Chloros, meaning "pale green"), is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 17. As part of common salt and other compounds, it is abundant in nature and necessary to most forms of life, including the human body. As chlorine gas, it is greenish yellow, is two and one half times as heavy as air, has an intensely disagreeable suffocating odor, and is exceedingly poisonous. In its liquid and solid form it is a powerful oxidizing, bleaching, and disinfecting agent.

The chemical processes for extraction of chlorine gas

Chlorine can be manufactured via the electrolysis of a sodium chloride solution, ie. brine. There are three methods for the extraction of chlorine by electrolysis used industrially.

Related Topics:
Electrolysis - Brine

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Mercury cell electrolysis

Mercury cell electrolysis was the first method used to produce chlorine on an industrial scale. Titanium anodes are located above a liquid mercury cathode, a solution of sodium chloride is positioned between the electrodes. When an electrical current is applied, chloride is released at the titanium anodes, whilst the sodium dissolves into the mercury cathode forming an amalgam.

Related Topics:
Mercury - Electrolysis - Titanium - Anode - Sodium chloride

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The amalgam can be regenerated into mercury by reacting it with water, producing hydrogen and sodium hydroxide. These are useful byproducts.

Related Topics:
Amalgam - Regenerated - Hydrogen - Sodium hydroxide

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This method consumes vast amounts of energy and there are also concerns about mercury emissions.

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Diaphragm cell electrolysis

An asbestos diaphragm is deposited on an iron grid cathode preventing the chlorine forming at the anode and the sodium hydroxide forming at the cathode from re-mixing.

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This method uses less energy than the mercury cell, but the sodium hydroxide is not as easily concentrated and precipitated into a useful substance.

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Membrane cell electrolysis

The electrolysis cell is divided into two by a membrane acting as an ion exchanger. Saturated sodium chloride solution is placed in the anode compartment whilst distilled water is placed in the cathodes compartment.

Related Topics:
Ion exchange - Distilled

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This method is nearly as efficient as the diaphragm cell and produces very pure sodium hydroxide.

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Other methods

In a laboratory, small amounts of chlorine gas can be created by adding concentrated hydrochloric acid (typically about 5M) to sodium chlorate solution.

Related Topics:
Hydrochloric acid - Sodium chlorate

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